Membrane-mediated interactions of rod-like inclusions.

Inclusions embedded in lipid membranes undergo a mediated force, due to the tendency of the membrane to relax its excess of elastic energy. In this paper we determine the exact shape of a two-dimensional vesicle hosting two different inclusions, and we analyse how the inclusion conformation influences the mediated interaction. We find non-trivial equilibrium configurations for the inclusions along the hosting membrane, and we derive the complete phase diagram of the mediated interaction. In particular, we find a non-vanishing mediated force even when the distance between the inclusions is much greater than their size. Our model can be applied to describe the mediated interactions of parallel, elongated inclusions embedded in three-dimensional membranes.

[Human papillomavirus associated with uterine cervix lesions]. / Papilomavírus humano associado a lesões de cérvice uterina.

It was studied the prevalence of human papillomavirus (HPV) among 228 women with lesions of uterine cervix attending the Ofir Loiola Institute, in Belem, Para, from March 1992 to May 1996. Histopathological examination was performed with all cervical biopsy samples obtained from these patients. In addition, specimens were analysed by both polimerase chain reaction and dot-blot hybridization to detect HPV DNA. The patients were assigned to three groups, according to the diagnosis made by histopathology, as follows: A, including 155 women suffering from invasive epidermoid carcinoma or adenocarcinoma; B, 54 patients having either cervical intraepithelial neoplasia grade II or III; and C, involving 19 women with chronic cervicitis. The prevalence rates of HPV in groups A, B and C were 70.3%, 63% and 36.8% respectively. HPV 16 accounted for 60.4% and 54.5% of types identified in groups A and B, respectively. Altogether HPV types 16, 18 and 33 were detected in 71.4% of positive patients belonging to group C.

[The application of the multileaf collimator in radiotherapy: the dosimetric problems and the technical implications for its clinical use]. / Applicazione del collimatore multilamellare nella radioterapia: problematiche dosimetriche e implicazioni tecniche per l'uso clinico.

INTRODUCTION: The multileaf collimator (MLC) now commercially available as an integral or optional retrofit component of linear accelerator heads, permitting to shield automatically irregular fields by computerized movements of multiple tungsten leaves. In the present paper we discuss the main characteristics of different MLC versions, MLC dosimetric drawbacks and the clinical fields where the MLC could he widely used. MATERIALS AND METHODS: Since February, 1995, we have studied the dosimetric characteristics and clinical implications of a multileaf collimator of a Clinac 2100 C/D linear accelerator used to replace conventional low melting alloy blocks. The scalloping effect of isodoses and the effective penumbra produced by the multileaf collimator in an irregular field were analyzed accurately. Secondly, radiation leakage through tungsten leaves was measured and compared with the values of low melting alloy blocks. Finally, the MLC was extensively used in clinical practice for the radiotherapy of different tumors. RESULTS: Different dosimetric steps were followed to obtain the monitor units/dose ratio. Our single MLC-shielded irregular fields measurements also showed several physical and dosimetric disadvantages related to wider effective penumbra than with conventional shielding when the angle between field margin and the normal to the direction of leaf travel is 45 degrees. In clinical practice, the MLC can be widely used for the conformal radiotherapy of pelvic and thoracic tumors. Conventional low melting alloy blocks should be replaced with MLC for radiotherapy of selected brain and head and neck cancers. DISCUSSION: The current use of a multileaf collimator improves both the accuracy and the effectiveness of radiation therapy and reduces the time for every treatment dose, which potentially increases the number of patients treated every day. The multileaf collimator is presently an important technical tool either to replace conventional shielding for static conformational radiotherapy or to administer 3D-planned dynamic radiotherapy.